The invention concerns a method for manufacturing a magnet coil configuration using a band-shaped conductor, which is slit in the longitudinal direction except for its two end areas such that the band-shaped conductor has a first and a second half band and two end areas that connect these half bands to form a closed loop.
A method of this type is disclosed in WO 2007/004787 A2.
Superconducting magnet coils are used for generating strong magnetic fields. The current that flows in the superconducting magnet coils is thereby practically carried without ohmic losses. Magnet coils that are wound with wires made from conventional low-temperature superconductors (LTS) such as NbTi or Nb3Sn have been used in a plurality of ways in practice, in particular, in NMR spectroscopy and imaging NMR. The magnetic field strength thereby limits the respective resolution.
In order to further increase the magnetic field strength that can be generated, it is globally tried to use high-temperature superconductors (HTS) in superconducting magnet coils. In comparison with LTS materials, HTS materials basically provide higher magnetic field strengths (also more than 20 Tesla) at the same low temperature (in most cases around 4 K). At higher temperatures (approximately 15 to 50K), at which typical LTS materials are already normally conducting, HTS materials still generate high field strengths (5 to 15 Tesla).
However, HTS materials generally have ceramic properties and have a layered crystal structure. The properties of the HTS materials (including the current carrying capacity) highly depend on the direction relative to the orientation of the layered crystal (anisotropy). Up to now, it has turned out to be advantageous in practice to use HTS materials in layers (often in the form of very thin layers) as part of band-shaped conductors.
In recent years, the manufacture and the quality of band-shaped HTS conductors, in particular, of the so-called YBCO-coated conductors could be considerably improved. For this reason, winding configurations and winding methods that are suited for band-shaped conductors, are becoming more important for the manufacture of magnet coils using HTS materials.
Some high-field applications require short-circuited superconducting magnet coils with extremely small loop resistance (typically smaller than 10 pΩ). However, these small loop resistances cannot be realized at present with superconducting joints (also called splices) of band-shaped HTS conductors.
WO 2007/004787 A2 discloses a way of bypassing the connection problem of bands with a continuous superconducting layer by means of a slit along the band. The half bands generated in this fashion are connected via non-slit end areas such that a continuous loop is generated for a superconducting current path. WO 2007/004787 A2 proposes winding of one flat coil with each half band to configure one superconducting electromagnet. One of the flat coils is subsequently rotated through 180° such that the magnetic fields of the two flat coils add during operation. In this connection, at least one of the half bands is substantially twisted in the two end areas. The resulting mechanical stress can damage the conductor, thereby impairing the current-carrying capacity and therefore also reducing the magnetic field that can be achieved. For larger solenoid-like coils, this document proposes to slit the band several times in the longitudinal direction and to wind one flat coil for each partial band.
J. Kosa et al. “Application Possibilities with Continuous YBCO Loops Made of HTS wire”, Journal of Physics: Conference Series 234 (2010), 032030, disclose a winding configuration for a band-shaped superconductor that is slit in its longitudinal direction except for its end areas, wherein the end areas are not twisted. Several serial loops are thereby formed from a conductor loop, which are then guided through each other. This method is difficult and only practicable for a small number of loose windings, and is, in particular, not suited for providing windings on a winding body.
U.S. Pat. No. 7,566,684 discloses a method, wherein two branches of a slit tape are wound onto a single mandrel, resulting in a double pancake coil. The branches are only linked at one end and do not form a closed conductor loop.
It is the underlying purpose of the invention to provide a simple method for winding a slit band-shaped conductor to form a magnet coil configuration which can also generate strong magnetic fields.